djm-fix.cpp
author František Kučera <franta-hg@frantovo.cz>
Mon, 04 Jan 2021 13:38:08 +0100
branchv_0
changeset 11 5b351628a377
parent 10 4d95b089457d
child 12 15d87fdd6e6c
permissions -rw-r--r--
Find card by a name pattern (regular expression) instead using hardcoded name.
By default, we look for card with name matching the "Pioneer DJ.*" pattern and we expect exactly one card to be found.
Custom pattern can be provided as a command-line argument.

Whole name would look something like this: "Pioneer DJ Corporation DJM-250MK2 at usb-0000:01:00.0-10.1, high speed".
     1 /**
     2  * DJM-Fix
     3  * Copyright © 2020 František Kučera (Frantovo.cz, GlobalCode.info)
     4  *
     5  * This program is free software: you can redistribute it and/or modify
     6  * it under the terms of the GNU General Public License as published by
     7  * the Free Software Foundation, version 3 of the License.
     8  *
     9  * This program is distributed in the hope that it will be useful,
    10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
    11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    12  * GNU General Public License for more details.
    13  *
    14  * You should have received a copy of the GNU General Public License
    15  * along with this program. If not, see <http://www.gnu.org/licenses/>.
    16  */
    17 
    18 #include <memory>
    19 #include <iostream>
    20 #include <chrono>
    21 #include <thread>
    22 #include <csignal>
    23 #include <atomic>
    24 
    25 #include "DJMFix.h"
    26 #include "AlsaBridge.h"
    27 
    28 static std::atomic<bool> run{true};
    29 
    30 void interrupt(int signal) {
    31 	run = false;
    32 	std::cerr << "interrupt()" << std::endl; // TODO: do not mess STDIO
    33 }
    34 
    35 /**
    36  * The support for Pioneer DJ DJM-250MK2 (an external USB sound card / mixer) was added to the Linux (kernel) by these patches:
    37  *
    38  *  - https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/sound/usb?id=73d8c94084341e2895169a0462dbc18167f01683 (playback)
    39  *  - https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/sound/usb?id=14335d8b9e1a2bf006f9d969a103f9731cabb210 (recording)
    40  *  - https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/sound/usb?id=cdc01a1558dedcee3daee7e1802d0349a07edb87 (mixer setup)
    41  *
    42  * These patches are enough for playback and for recording from post CH faders.
    43  *
    44  * However this mixer is somehow incapacitated and if we want to record the raw signal from the PHONO or LINE channels,
    45  * we only get silence. This feature is important for DVS (Digital Vinyl Systems) setups where
    46  * the timecode signal from special control vinyls flows from mixer to the computer
    47  * where it is interpreted in a software like MIXXX and used for controlling the playback of files on our computer.
    48  * The signal (usually music) from these files flows back to the mixer and then to speakers and headphones.
    49  *
    50  * To make this work and enjoy all the features of the device we have bought, we need to tell the mixer that we
    51  * want the signal instead of silence on given channels. And this is the purpose of the djm-fix utility and
    52  * it is done by sending some magic packet to the mixer.
    53  *
    54  * Implementation of this magic in the AlsaBridge.cpp file is based on publicly available documentation
    55  * that can be found at <https://mixb.me/CDJHidProtocol/hid-analysis/handshake.html>.
    56  * This page pointed me to the proper hash function (according to the constants, it is bit uncommon but publicly known Fowler–Noll–Vo hash function, FNV)
    57  * and some magic bits. I wrote this standalone C++ program that talks with the mixer over MIDI SysEx messages and does the magic.
    58  *
    59  * When this program is started, it finds the mixer and makes it fully working.
    60  * It needs to be running all the time, otherwise we will get silence on the PHONO/LINE channels again.
    61  *
    62  * Install dependencies:
    63  *   apt install mercurial make pkg-config g++ libasound2-dev    # in Debian or Ubuntu (it will be similar in other distributions)
    64  *
    65  * Download djm-fix:
    66  *   hg clone https://hg.frantovo.cz/midi/djm-fix/               # primary source
    67  *   hg clone https://hg.globalcode.info/midi/djm-fix/           # or we can use this mirror
    68  *
    69  * Compile:
    70  *   make                                                        # we can skip this step, it will be compiled on the first run
    71  *
    72  * Run:
    73  *   make run                                                    # in most cases
    74  *   build/djm-fix 'Pioneer DJ.*'                                # or provide custom name pattern (regular expression) to select the proper card
    75  *
    76  * Stop:
    77  *   press Ctrl+C
    78  * 
    79  * Look for updates in the Mercurial repositories and at <https://blog.frantovo.cz/c/387/>.
    80  */
    81 
    82 int main(int argc, char**argv) {
    83 	try {
    84 		std::string cardNamePattern = argc == 2 ? argv[1] : "Pioneer DJ.*";
    85 
    86 		signal(SIGINT, interrupt);
    87 		std::unique_ptr<djmfix::DJMFix> djmFix(djmfix::create());
    88 		std::unique_ptr<djmfix::alsa::AlsaBridge> alsaBridge(djmfix::alsa::create(djmFix.get(), cardNamePattern));
    89 
    90 		alsaBridge->start();
    91 		while (run) std::this_thread::sleep_for(std::chrono::milliseconds(100));
    92 		alsaBridge->stop();
    93 
    94 		return 0;
    95 	} catch (const std::exception& e) {
    96 		std::cerr << "ERROR: " << e.what() << std::endl; // TODO: do not mess STDIO
    97 	}
    98 }